1. Field of the Invention
The present invention relates to a system and method for monitoring engine performance characteristics and, more particularly, pertains to a system and method for monitoring occurrences of knocks in an internal combustion engine and identifying knocking cylinders of the engine.
2. Description of the Related Art
Under wide-open throttle conditions, an engine is most susceptible to knock. A direct constraint on engine performance, knock also constrains engine efficiency by limiting the engine compression ratio. Knock depends upon both the quality of fuel and the engine design.
FIGS. 11A, 11B and 11C illustrate the in-cylinder pressure variations during normal combustion, light knock, and heavy knock, respectively. With light knock (FIG. 11B), knock occurs late in the burning process and the amplitude of the pressure fluctuations is relatively small. With heavy knock (FIG. 11C), knock occurs closer to the top-center earlier in the combustion process and the initial amplitude of the pressure fluctuation is significantly higher.
Prior knock detection systems include systems employing piezoelectric pressure transducers positioned at the end-gas region of the combustion chamber. There are several problems with such systems. First, it requires a pressure sensor for each cylinder of the engine which drives up the cost and complexity of the system. Second, precise positionings of the pressure transducers within the combustion chambers are required because transducers positioned at different points in the chamber will record different pressure levels at a given time due to the shock wave propagation phenomena (caused by the spontaneous release of much of the chemical energy of the end-gas fuel) characteristic of knock.
Other prior knock detection systems employ a vibration-driven accelerometer mounted on the block of the engine. The performance of such systems, however, is plagued by a high incidence of "false knock" indications. Furthermore, the performance of such systems is highly dependent upon the placement of the accelerometer on the engine block.